Method of encoding/decoding data, method of detecting data, and method of recording/reproducing data

ABSTRACT

A data encoding method is provided. In this method, a plurality of n-bit input codes is converted into a plurality of M L block codes, wherein every bit in each of the block codes has at least one identical bit adjacent horizontally or vertically to the bit.

TECHNICAL FIELD

The present invention relates to a method for encoding and decodingdata, a method for detecting data, and a method forrecording/reproducing data using the same, and more particularly, to amethod for encoding and decoding holographic data using a holographicstorage device, a method for detecting data, and a method for recordingand reproducing data.

BACKGROUND ART

Recording of data on a holographic storage device is performed byrecording the intensity and direction of signal light reflected from atarget object. The signal light from the target object interferes withreference light to produce an interference fringe corresponding to theintensity and direction of the signal light and the producedinterference fringe is then recorded in a holographic storage mediumincluding a material that reacts to the light according to the intensityof the interference fringe. Data recorded in the storage medium can beread using the reference light used in the process for recording thedata and cannot be read using reference light with a wavelength andphase different from those of the reference light used for recordingsince the reference light with a different wavelength and phase passesthrough the data recorded in the recording medium.

Utilizing these holographic characteristics, a large amount of data canbe recorded at the same place in a recording medium using differentreference light beams, thereby enabling storage of a large amount ofdata in a small recording medium.

Generally, input data is modulated in order to record the data in arecording medium while minimizing the influence of ambient noise and toaccurately reproduce the recorded data. Thus, the holographic storagedevice also uses a modulation code in order to correctly record andreproduce data.

In the holographic storage device, the modulation code needs to bedesigned so as to prevent the occurrence of Inter-Page Interference(IPI) which is interference between adjacent data pages and Inter-SymbolInterference (ISI) which is interference between pixels in a page when adata page is recorded in a medium.

DISCLOSURE OF INVENTION Technical Problem

An object of the present invention devised to solve the problem lies onproviding a method for encoding and decoding data, which can reduce IPIand ISI, and a method for recording and reproducing data using the same.

TECHNICAL SOLUTION

The object of the present invention can be achieved by providing a dataencoding method for converting a plurality of n-bit input codes into aplurality of M×L block codes, wherein every bit in each of the blockcodes has at least one identical bit adjacent horizontally or verticallyto the bit.

Here, the plurality of block codes may have the same ratio between thenumber of 0s and the number of 1s. In this case, each of the block codesmay be a 3″3 block code including five 0s and four 1s.

In addition, each of the block codes may be a 4″4 block code includingeight 0s and eight 1s, ten 0s and six 1s, or nine Os and seven 1s.

In addition, each of the block codes may include an odd number of bits,and bits other than a bit located at a center of the block code may havethe same number of bit values of 0 and 1. Here, the block code may be a3″3 block code.

In this case, the number of the block codes may be greater than or equalto the number of possible values of the input code.

In another aspect of the present invention, provided herein is a datadetection method for detecting data from data images corresponding tobits included in an encoded block code, wherein every bit in the blockcode has at least one identical bit adjacent horizontally or verticallyto the bit, and bit values of the block code are defined according torelative brightness of the data images.

A bit corresponding to a relatively light data image among the dataimages may be defined as “1” and a bit corresponding to a relativelydark data image among the data images may be defined as “0”.

The block code may include an odd number of bits, and bits other than abit located at a center of the block code may have the same number ofbit values of 0 and 1.

In this case, the data detection method may include obtaining an averagebrightness level of data images corresponding to “0” and an averagebrightness level of data images corresponding to “1”, comparing theaverage brightness levels with a brightness level of a data imagecorresponding to the bit located at the center of the block code, anddetermining that a bit value corresponding to one of the averagebrightness level of the data images corresponding to “0” and the averagebrightness level of the data images corresponding to “1”, the one of thetwo average brightness levels being closer to the brightness level ofthe data image corresponding to the bit located at the center, is a bitvalue of the bit located at the center.

In another aspect of the present invention, provided herein is a datadecoding method for converting a plurality of M×L block codes into aplurality of n-bit codes, wherein every bit in each of the block codeshas at least one identical bit adjacent horizontally or vertically tothe bit.

In another aspect of the present invention, provided herein is a datarecording method including encoding an input code into a block code, andstoring the block code in a recording medium, wherein every bit in theblock code has at least one identical bit adjacent horizontally orvertically to the bit.

In another aspect of the present invention, provided herein is a datareproduction method including reading a block code from a recordingmedium, and converting the block code into a demodulation code, whereinevery bit in the block code has at least one identical bit adjacenthorizontally or vertically to the bit.

ADVANTAGEOUS EFFECTS

The data encoding/decoding method according to the present invention canprevent interference between adjacent pages and interference betweenadjacent symbols. The data detection method according to the presentinvention can reduce the occurrence of errors during signal detection.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate exemplary embodiments of theinvention and together with the description serve to explain theprinciple of the invention.

In the drawings:

FIG. 1 schematically illustrates an example of an apparatus forrecording and reproducing data which can perform a dataencoding/decoding method according to an exemplary embodiment of thepresent invention.

FIG. 2 schematically illustrates an example of block codes that can beused in a data encoding/decoding method according to a first exemplaryembodiment of the present invention.

FIG. 3 schematically illustrates another example of block codes that canbe used in the data encoding/decoding method according to the firstexemplary embodiment of the present invention.

FIG. 4 schematically illustrates an example of data images of blockcodes that can be used in a data encoding/decoding method according to asecond exemplary embodiment of the present invention.

FIG. 5 schematically illustrates pixels of block codes to explain amethod for determining a bit value of a central pixel in the dataencoding/decoding method according to the second exemplary embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The above and other aspects of the present invention will be describedin detail through exemplary embodiments with reference to theaccompanying drawings so that the present invention can be easilyunderstood and realized by those skilled in the art.

FIG. 1 schematically illustrates an example of a holographicrecording/reproduction system that can perform a data encoding/decodingmethod according to an exemplary embodiment of the present invention. Asshown in FIG. 1, the holographic recording/reproduction system includesa recording/reproduction apparatus 100, a data encoding device 200, anda data decoding device 300.

The recording/reproduction apparatus 100 includes a light source 10 forgenerating a laser beam required in holography, a storage medium 12 (forexample, a photorefractive crystal) for storing three-dimensional data(i.e., an interference fringe), and a Charged Coupled Device (CCD) 14.Two paths (i.e., a reference light processing path PS1 and a signallight processing path PS2) including a number of optical systems areformed between the light source 10 and the storage medium 12.

The optical splitter 16 splits the laser beam incident from the lightsource 10 into reference light and signal light. The split referencelight, which is vertically polarized, is provided to the reference lightprocessing path PS1 and the split signal light is provided to the signallight processing path PS2.

The shutter 18, the reflector 20, and the actuator 22 are arrangedparallel to the emission direction of the reference light in thereference light processing path PS1. In the reference light processingpath PS1, reference light required to record or reproduce data isreflected at a preset deviation angle to be provided to the storagemedium 12.

Although not illustrated in FIG. 1, a number of optical lenses (forexample, a waist creation lens and a beam expander) for reference lightprocessing may be provided in the reference light processing path PS1.

The vertically polarized reference light incident via the shutter 18after being deviated from the optical splitter 16 is adjusted through anoptical lens or the like so that the sectional beam size of thereference light is increased to a specific size. The reference lightthen deviates at a preset angle (for example, a recording angle presetfor recording or a reproduction angle preset for reproduction) throughthe reflector 20 and is then emitted to the storage medium 12.

Here, the reference light used during recording or reproduction can becontrolled by rotating the reflector 20 using the actuator 22 to changethe deviation angle thereof each time binary data of each page isrecorded in the storage medium 12. Through this reference lightdeviation method, hundreds or thousands of pieces of data can be storedor read in or from the storage medium 12.

On the other hand, a shutter 24, a reflector 26, and a spatial lightmodulator 28 are sequentially arranged parallel to the emissiondirection of the signal light in the signal light processing path PS2.The shutter 24 is kept open in a recording mode and is kept closed in areproduction mode under control of a system controller (not shown).

Although not illustrated in FIG. 1, a number of optical lenses (forexample, a reimaging lens, a beam expander, and a field lens) for signallight processing may be provided in the signal light processing pathPS2. Accordingly, the signal light incident through an opening of theshutter 24 after being deviated from the optical splitter 16 isreflected at a preset deviation angle through the reflector 26 and isthen provided to the spatial light modulator 28.

The spatial light modulator 28 modulates the signal light received fromthe reflector 26 into a binary data image including light and darkpixels according to input data provided from the data encoding device200 (i.e., according to data encoded using a data encoding methodaccording to the embodiment of the present invention that is describedlater). Here, pixels of the data image correspond respectively to bitsincluded in a block code described later.

For example, when the input data is image data of a frame of a picture,the signal light incident on the spatial light modulator 28 is modulatedinto signal light of the frame and the modulated signal light is thenincident on the storage medium 12 in synchronization with the referencelight incident from the reflector 20 in the reference light processingpath PS1.

Accordingly, an interference fringe obtained through interferencebetween the signal light modulated for each page of the binary dataimage provided from the spatial light modulator 28 in the recording modeand the corresponding reference light for recording that is incidentfrom the reflector 20 at a deviation angle is recorded in the storagemedium 12. That is, photoinduction of mobile charges occurs inside thestorage medium 12 according to the intensity of the interference fringeobtained by the interference between the modulated signal light and thereference light and the interference fringe of data is recorded in thestorage medium 12 through this process.

On the other hand, the data encoding device 200 separates an inputsequence received from the outside into n-bit blocks and converts eachn-bit block of the input sequence into a corresponding M×L-bit blockcode according to an encoding method according to the embodiment of thepresent invention. This encoding method will be described later.

The data encoding device 200 transfers binary data of one page encodedin this manner to the spatial light modulator 28. Accordingly, thespatial light modulator 28 modulates the signal light incident from thereflector 26 for each page of the binary data including light and darkpixels and emits the modulated signal light to the storage medium 12. Inthis manner, data coded according to the present invention is stored inthe storage medium 12.

On the other hand, when data, which is recorded in the storage medium 12after being coded according to the encoding method according to theembodiment of the present invention, is reproduced, the shutter 24 ofthe signal light processing path PS2 is closed under control of thesystem controller (not shown) while the shutter 18 of the referencelight processing path PS1 is opened.

Accordingly, the reference light (reference light for reproduction)deviated from the optical splitter 16 is reflected at the reflector 20to be emitted to the storage medium 12. The interference fringe that hasbeen recorded in the storage medium 12 through the reference light forrecording diffracts the reference light for reproduction incident on thestorage medium 12 to demodulate the interference fringe into a binarydata signal of one page including original light and dark pixels (incheckerboard patterns) and the demodulated reproduction signal is thenemitted to the CCD 14.

The CCD 14 reconstructs original data (i.e., an original electricsignal) from the reproduction light emitted from the storage medium 12and the reconstructed reproduction signal is then transferred to thedata decoding device 300.

The data decoding device 300 decodes the coded reproduction signal thatis output through the CCD 14 after being reproduced from the storagemedium 12 into original data as present prior to coding (i.e., the inputsequence signal described above). This decoding method will be describedlater.

Although the configuration of the holographic recording/reproductionsystem has been illustrated, the present invention is not limited tothis configuration and other components may be added to or somecomponents may be omitted from the holographic recording/reproductionsystem as needed.

Reference will now be made in detail to an encoding method and adecoding method according to an exemplary embodiment of the presentinvention. An n-bit input sequence is modulated into an M×L-bit channelsequence in the encoding method according to the embodiment of thepresent invention and an M×L-bit channel sequence is demodulated into ann-bit input sequence in the decoding method according to the embodimentof the present invention. Here, an array of M×L bits with M bitsarranged in a horizontal direction and L bits arranged in a verticaldirection is defined as a block code.

FIGS. 2 and 3 schematically illustrate example block codes that can beused in an encoding/decoding method according to a first exemplaryembodiment of the present invention. FIG. 2 illustrate 3×3 block codes,each of which is used to modulate a 5-bit input sequence into a 9-bitchannel sequence and FIG. 3 illustrate 4×4 block codes, each of which isused to modulate a 10-bit input sequence into a 16-bit channel sequence.

However, the present invention is not limited to the example block codesshown in FIGS. 2 and 3 and encoding/decoding may be performed usingblock codes of various other sizes.

Constraints of a block code used to convert an n-bit input sequence intoan M×L-bit channel sequence in this embodiment will now be described indetail with reference to FIGS. 2 and 3.

First, the number of possible values of an n-bit input sequence is 2n.In addition, the number of possible values of an M×L-bit input sequenceis 2M×L. That is, in the above example, the number of possible values ofthe 5-bit input sequence is 25=32 and the number of possible values ofthe 9-bit channel sequence is 29=512. In addition, the number ofpossible values of the 10-bit input sequence is 210=1024 and the numberof possible values of the 16-bit channel sequence is 216=65536.

Here, in the encoding method according to this embodiment, every bit ina block code has at least one identical bit adjacent horizontally orvertically to the bit. That is, the same bit is repeated at least oncein a horizontal or vertical direction in the block code. The block codehas no isolated bit since the same bit is repeated at least once in ahorizontal or vertical direction. That is, as shown in FIGS. 2 and 3,there is no 0 surrounded by 1s and there is no 1 surrounded by 0s.Accordingly, when a block code is converted into a binary data imageincluding light and dark pixels, it is possible to prevent each pixelfrom suffering from inter-symbol interference with adjacent symbols(i.e., pixels).

The encoding method according to this embodiment uses block codes, eachof which includes x 0s and (M×L)−x 1s, among 2M×L block codes. That is,the block codes have the same ratio between the number of 0s and thenumber of 1s. Due to this constraint, the intensity of light of eachpage of a data image, which includes a plurality of block codes asdescribed above, is similar. Thus, the constraint can prevent inter-pageinterference (IPI) between adjacent data pages.

FIG. 2 illustrates an example where the number of 0s is 5 and the numberof 1s is 4 and FIG. 3 illustrates an example where the number of 0s is10 and the number of 1s is 6. However, the present invention is notlimited to these examples. Especially, a 4″4 block code may include 8 0sand 8 1s or 9 0s and 7 1s, unlike 4″4 block codes illustrated in FIG. 3.That is, it is preferable that the number of 0s and the number of 1s ina block code be similar. Accordingly, each page has pseudo-balancedmodulation code characteristics.

In this embodiment, the number of channel sequences satisfying the twoconstraints for each block code among 2M×L channel sequences should begreater than or equal to the number of 2n possible values of the n-bitinput sequences. According to the constraints, each of the block codesof FIG. 2 includes 5 0s and 4 1s and the same bit is repeated at leastonce in each block code. The number of block codes satisfying theconstraints among a total of 512 possible block codes is 32, which isequal to the number of possible values of the 5-bit input sequence.

In the case of FIG. 3, block codes, each of which includes 10 0s and 61s, are used among a total of 65536 possible block codes. The number ofblock codes satisfying the constraint that the same bit be repeated atleast once in a horizontal or vertical direction is 1070. This number ofblock codes is greater than the number of possible values of a 10-bitinput sequence (i.e., 1024), thereby satisfying the constraint describedabove.

Accordingly, such block codes can prevent IPI and ISI since theintensity of light of each page is similar and there is no isolated bit.

Reference will now be made to a data detection method and a decodingmethod according to the first exemplary embodiment of the presentinvention.

As described above, when encoded data recorded in a recording medium isreproduced, an interference fringe that has been recorded in the storagemedium 12 through the reference light for recording diffracts thereference light for reproduction incident on the storage medium 12 todemodulate the interference fringe into a binary data signal of one pageincluding original light and dark pixels (in checkerboard patterns).

The CCD decodes an M×L-bit reproduction signal reconstructed in thismanner into original data as present prior to coding, i.e., an n-bitinput sequence described above.

First, reference is made in detail to a method for detecting a datasignal from a data image including light and dark pixels according tothe first exemplary embodiment of the present invention.

As described above, in this embodiment, block codes have the same numberof 0s and the same number of 1s. That is, (M×L)−x 1s and x 0s aredistributed in each block code. Utilizing this fact, (M×L)−x bitsselected in order of decreasing brightness (i.e., decreasing gray level)of the data image are defined as “1 (i.e., light)” and the remaining xbits are defined as “0 (i.e., dark)”.

Specifically, in the case of FIG. 2, 4 pixels with high gray levelsamong 9 data image pixels are defined as “1” and the remaining 5 pixelsare defined as “0”. In the case of FIG. 3, 6 bits (pixels) with highgray levels among 16 pixels are defined as “1” and the remaining 10 bitsare defined as “0”. This signal detection method reduces the possibilityof error occurrence, compared to the case where bits are defined basedon a specific reference level.

Then, an M×L-bit block code signal detected in this manner is convertedinto a corresponding demodulation code (i.e., an n-bit input sequence),thereby decoding data. The decoding method in this embodiment performsthe reverse of encoding using the code block.

Reference will now be made in detail to encoding and decoding methodsand a data detection method according to a second exemplary embodimentof the present invention. In the encoding method according to thisembodiment, every bit in a block code has at least one identical bitadjacent horizontally or vertically to the bit, similar to the firstembodiment described above. That is, the same bit is repeated at leastonce in a horizontal or vertical direction in the block code. Thisprevents the occurrence of ISI as described above.

On the other hand, a block code has an odd number of bits in theencoding method according to this embodiment. In addition, among the oddnumber of bits, bits other than a bit located at the center of the blockcode have the same number of 0s and 1s. In this case, the bit located atthe center may be 0 or 1. Thus, unlike the first exemplary embodiment,block codes of this embodiment have different ratios between 0s and 1s.The ratio between 0s and 1s varies according to the bit located at thecenter.

FIG. 4 illustrates data images of 3″3-bit block codes as the data imagesof the block codes in the encoding/decoding method according to thesecond exemplary embodiment of the present invention. This embodimentwill now be described in detail with reference to FIG. 4.

As illustrated in FIG. 4, 9 bits are arranged in a matrix of 3″3 bits sothat the number of “1” bits and the number of “0” bits other than a bitlocated at the center are each 4. Accordingly, the peripheral bits havebalanced characteristics.

However, a difference is made according to whether the bit value of thebit located at the center is 1 or 0. Accordingly, block codes accordingto this embodiment have pseudo-balanced characteristics.

A method for detecting data coded using the encoding method according tothe second exemplary embodiment of the present invention and a methodfor decoding the detected data are described below in detail.

First, reference is made to the data detection method according to thisembodiment. A data image reproduced from a holographic storage device iscorrected and the corrected data image is then converted into acorrected gray level.

First, bit values of peripheral bits located around a bit located at thecenter are determined. As described above, peripheral bits of a blockcode according to this embodiment have the same number of 0s and 1s.Accordingly, each pixel with a high gray level (i.e., a light pixel) isdefined as “1” and each pixel with a low gray level (i.e., a dark pixel)is defined as “0”.

That is, the bit values of 4 bits with high gray levels among bitscorresponding to data images of peripheral pixels other than a pixellocated at the center are determined to be “1” and the bit values of 4bits with low gray levels are determined to be “0”.

Then, the bit value of the pixel located at the center is determined.The bit value of the pixel located at the center can be determined usingvarious methods. An example method for determining the bit value of thepixel located at the center is described below with reference to FIG. 5.

As shown in FIG. 5, respective gray levels of the corrected pixels aredefined as a, b, c, d, e, f, g, h, and i.

First, an average gray level mlight of four pixels selected in order ofdecreasing brightness from among peripheral bits is calculated. In theexample of FIG. 5, mlight is (f+g+e+d)/4. In addition, an average graylevel mdark of four pixels selected in order of increasing brightnessfrom among the peripheral bits is calculated. In the example of FIG. 5,mdark is (a+b+c+d)/4. Then, respective Euclidean distances between thegray level (i) of the central bit and the two average gray levels arecalculated.

Here, when the Euclidean distance between the gray level (i) of thecentral bit and the average gray level mlight is denoted by “A” and theEuclidean distance between the gray level (i) of the central bit and theaverage gray level mdark is denoted by “B”, “A” can be represented byMathematical Expression 1 and “B” can be represented by MathematicalExpression 2.

abs(i−m _(light))  MATHEMATICAL EXPRESSION 1

abs(i−m _(dark))  MATHEMATICAL EXPRESSION 2

When A is greater than B, i.e., when the gray level (i) of the pixellocated at the center is closer to the average gray level mlight of thelight pixels, the bit value of (i) is defined as “1 (light)”. On theother hand, when B is greater than A, i.e., when the gray level (i) ofthe pixel located at the center is closer to the average gray levelmdark of the dark pixels, the bit value of (i) is defined as “0 (dark)”.

The bit value of the central pixel is defined using this method. A datasignal is detected using this method to generate a code block accordingto the second exemplary embodiment of the present invention. The datadecoding method according to this embodiment is a procedure forconverting the code block generated in this manner into an originalinput sequence. This procedure is performed according to the reverse ofthe encoding method according to the second exemplary embodiment of thepresent invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A data encoding method for converting a plurality of n-bit inputcodes into a plurality of M×L block codes, wherein every bit in each ofthe block codes has at least one identical bit adjacent horizontally orvertically to the bit.
 2. The method of claim 1, wherein the pluralityof block codes have the same ratio between the number of 0s and thenumber of 1s.
 3. The method of claim 2, wherein each of the block codesis a 3″3 block code including five 0s and four 1s.
 4. The method ofclaim 2, wherein each of the block codes is a 4″4 block code includingeight 0s and eight 1s, ten 0s and six 1s, or nine 0s and seven 1s. 5.The method of claim 1, wherein the block codes includes an odd number ofbits, and bits other than a bit located at a center of the block codehave the same number of bit values of 0 and
 1. 6. The method of claim 5,wherein the block code is a 3″3 block code.
 7. The data encoding methodof claim 1, wherein the number of the block codes is greater than orequal to the number of possible values of the input code.
 8. A datadetection method for detecting data from data images corresponding tobits included in an encoded block code, wherein every bit in the blockcode has at least one identical bit adjacent horizontally or verticallyto the bit, and bit values of the block code are defined according torelative brightness of the data images.
 9. The method of claim 8,wherein a bit corresponding to a relatively light data image among thedata images is defined as “1” and a bit corresponding to a relativelydark data image among the data images is defined as “0”.
 10. The methodof claim 9, wherein the block code includes an odd number of bits, andbits other than a bit located at a center of the block code have thesame number of bit values of 0 and
 1. 11. The method of claim 10,comprising: obtaining an average brightness level of data imagescorresponding to “0” and an average brightness level of data imagescorresponding to “1”; comparing the average brightness levels with abrightness level of a data image corresponding to the bit located at thecenter of the block code; and determining that a bit value correspondingto one of the average brightness level of the data images correspondingto “0” and the average brightness level of the data images correspondingto “1”, the one of the two average brightness levels being closer to thebrightness level of the data image corresponding to the bit located atthe center, is a bit value of the bit located at the center.
 12. Themethod of claim 11, wherein the block code is a 3″3 block code.
 13. Adata decoding method for converting a plurality of M×L block codes intoa plurality of n-bit codes, wherein every bit in each of the block codeshas at least one identical bit adjacent horizontally or vertically tothe bit.
 14. The method of claim 13, wherein the plurality of blockcodes have the same ratio between the number of 0s and the number of 1s.15. The method of claim 14, wherein each of the block codes is a 3″3block code including five 0s and four 1s.
 16. The method of claim 14,wherein each of the block codes is a 4″4 block code including eight 0sand eight 1s, ten 0s and six 1s, or nine 0s and seven 1s.
 17. The methodof claim 13, wherein each of the block codes includes an odd number ofbits, and bits other than a bit located at a center of the block codehave the same number of bit values of 0 and
 1. 18. The method of claim17, wherein the block code is a 3″3 block code.
 19. A data recordingmethod comprising: encoding an input code into a block code; and storingthe encoded block code in a recording medium, wherein every bit in theblock code has at least one identical bit adjacent horizontally orvertically to the bit.
 20. A data reproduction method comprising:reading a block code from a recording medium; and converting the blockcode into a demodulation code, wherein every bit in the block code hasat least one identical bit adjacent horizontally or vertically to thebit.